Sear release mechanism



J. LOCHHEAD SEAR RELEASE MECHANISM 2 Sheets-Sheet 1 Filed Jan. 3, 1946 MM MMM W Feb. 22, 1949,

Filed Jan. 3, 19.46

J. 1.. LOCHHEAD 2,462,114

SEAR RELEASE MECHANISM 2 Sheets-Sheet 2 TJEI-ITLTL'YL L El (ah 11911 :1:

Patented Feb. 22, 1949 UNIT STA

SEAR RELEASE MECHANISM John L. Lochhead, Springfield, Mass, assignor to the United States of America as represented by the Secretary of War (Granted under the act of March 3, 1883, as

amended April 30, 1928; 370 0. G. 757) 1 Claim.

The invention described herein may be manufactured and used by or for the Government for governmental purposes, without the payment to me of any royalty thereon.

This invention relates to a sear release mechanism for a firearm of the automatic type and particularly to a sear release mechanism requiring but a slight force to effect release of such mechanism.

The scar release mechanism of automatic firearms must positively engage the hammer or the firing pin until such sear is released to permit the hammer to fall or the firing pin to go forwardly to efiect discharge of a cartridge. In order to obtain such positive engagement of the firing pin or hammer by the sear, relatively still springs and steep cocking angles are usually resorted to. The unfortunate result of such springs and steep camming or cockingangles produces an extremely hard sear release. Frequently a push or a pull of about 30 pounds is required to effect such release. It is readily apparent that such a large load places undue strain upon the mechanism utilized to release the sear and produces a heavy and irregular trigger pull.

Accordingly, it is an object of this invention to provide a scar release mechanism for an automatic firearm having a light sear release load.

It is a particular object of this invention to provide a sear release mechanism having a light sear release load for a firearm of the type known as the Browning machine gun.

Another object of this invention is to provide a sear release mechanism that can be readily assembled to the bolt of the firearm whereby release of such sear can be effected from either the right or left side of the firearm or from the top thereof.

The specific nature of the invention as well as other objects and advantages thereof will clearly appear from a description of a preferred embodiment as shown in the accompanying drawings in which:

Fig. 1 is an exploded perspective view of the related components of the sear mechanism.

Fig. 2 is a fragmentary longitudinal sectional view of a firearm bolt showing the firing pin held in the cocked position by the sear mechanism.

Fig. 3 is a rear end elevational view of a firearm bolt showing the sear components assembled thereto.

Fig. 4 is a detail longitudinal sectional view of the scar and sear bar showing the position of scar bar with respect to the sear.

5 is a top elevational detail view of the sear.

Fig. 6 is a side elevational detail view of the sear slide.

Fig. 7 is a fragmentary side elevational detail view of the firing pin and firing pin extension.

Fig. 8 is a perspective view of the sear spring.

Fig. 9 is a side elevational view of the sear slide shown partly in longitudinal section to illustrate the spring biased plunger secured thereto.

Fig. 10 is a detail view showing the sear bar in front elevation.

Fig. 11 is' a reduced fragmentary side elevational detail View of the firearm bolt showing the horizontal slot provided for the sear slide.

ihis invention will be described as applied to a sear which is utilized to hold a spring pressed firing pin in its cocked position. Such sear and firing pin are provided with sloped engaging surfaces which are disposed at such an angle that upon release of the sear the relatively strong force of the firing pin readily cams the sear upwardly out of engagement with such firing pin. The sear is restrained from moving upwardly by a transverse slide. Such slide engages a lug provided on the sear. A minimum engagement is provided between the sear and slide whereby only a comparatively light push is required to disengage such slide from the sear. Upon disengagement of the slide from the sear, the bias of the firing pin spring forces the firing pin forwardly to readily cam the sear out of engagement with the firing pin.

It is desired to point out that the sear release mechanism to be described herein is preferably utilized in a firearm or guns of the Browning type as disclosed in U. S. Patent No. 1,628,226 to John M. Browning. However, such mechanism is not limited to this particular type of firearm but may be utilized in any type of automatic firearm of a similar type having a recoiling breech member.

In Fig. 1 there is shown in assembled relation a firearm breech block I embodying this invention. Such breech member I is provided with the usual longitudinal hole 2 to accommodate a firing pin 3 and firing pin extension 4 referred to collectively as a firing device. A vertical longitudinally disposed recess 5 in the rear end of such block permits mounting a cocking lever 6 therein on a horizontal transverse pin 7. Such elements are equivalents of conventional elements disclosed in U. S. Patent No. 1,628,226 to John M. Browning and need not be further described herein. I

Recess 5 communicates with longitudinal hole 2 so that the lower end of cocking lever 6 can be shown at 38.

inserted within a slot 8 of firing pin extension 4 in order to cock such firing pin. A spring 9 is placed within the hollow interior of firing pin extension 4. Such spring abuts a transverse pin It provided in the forward end of firing pin extension 4. A pin retaining plunger I I which is provided with a head I2 is inserted in the rear end of spring 9. Plunger H bears against a vertical pin I3. Such pin is inserted in a vertical hole I4 in the breech block I and a head portion I3 thereof also functions to retain a scar spring 30 within recess 5. A transverse slot I6 is provided on the bottom of pin l3 so that when pin I3 is inserted in hole I4 and forced downwardly into assembled position, the head I2 of pin retaining plunger II will engage such slot to secure pin I3 within hole I4.

A sear I1 is mounted in oppositely disposed vertical slots I8 and IBa provided in recess 5 near the, rear end of breech block I as shown in Fig. l. Sear I1 is a substantially rectangular member. Parallel longitudinal ribs l5 and 29 areprovided on opposite sides of sear I? (Fig. 5), to engage vertical slots l8 and I8a. On the lower forward face of sear I? there is provided an integral tang 2| for a purpose that will be later described. On the bottom of sear ll, there is provided a sloped cam surface 22. Such sloped surface cooperates with a corresponding cam surface 23provided on the end of firing pin extension 4 as shown in Fig. 2. A transverse slot 24 is provided in sear H somewhat above the bottom thereof and a vertical slot 25 is provided therein as shown in Fig. 1. Slot 25 is provided to admit a. lug 26 on a sear bar 27 to project therethrough as will be later described. On the forwardly facing surface of sear ll, there is provided a transverse notch 29 at the top of such sear. Sear spring 30 rests on a shoulder 3| formed by notch 29 to force sear I? downwardly as will be later described.

A horizontal transverse slot 32 is provided in the rear of breech block I. Such slot perpendicularly intersects vertical slots I8 and i811. In slot 32 there are provided oppositely disposed guideways 33. A sear slide 34 comprising a substantially rectangular member is slidably mount- .edwithin slot 32. Oppositely disposed ribs 35 are provided on slide 34 which engages guideways 33 in slot 32 and one of which is adapted, for example the lower left rib 35, Fig. 3, to engage the surface defining the lower side of slot 24 in sear t'l so as to prevent upward movement of the sear when .the slide is so disposed as to have a rib thusly positioned to slidably secure slide 34 within slot 32. Such slide is further secured by a scar bar 21 to be described. The right end 36 of slide 34.- is enlarged as shown in Fig. 9 and a horizontal hole 31 is provided therein. The entering end of such hole is counterbored as ,A plunger 39 isv inserted in such hole and rests against the bottom thereof. Plunger 39 comprises a cup-like member and a spring 40;.is placed in the open end'of such plunger. Spring 49 isretained within hole 3'! by a suitable plug 4|, secured within the counterbored end 38 of hole 31 by a transverse pin 42. Spring biased plunger 39 functions to bias sear slide 34 to the right as shown inFig. 3 by engagement of the base of the plunger 39 against the side of scar I'I.

Two centrally located, oppositely disposed notches 43 and 44 are provided on sear slide, 34 to permit the sear 11 to .be forced upwardly into oneof suchnotches as willbe presently described. A sloped cam surface 45 is centrally provided on sear slide 34 as shown in Fig. 6. Such cam surface is provided to cooperate with a corresponding cam surface 46 provided on sear bar 21 as will be presently described. A notch 52 is provided on the bottom of sear slide 34 which is engaged by sear bar 21 when slide 34 is assembled in reverse for left side release as will be later described.

Sear bar 21 as viewed in Fig. 10 is a generally elongated element formed with a longitudinal rib 4'! on its left side and the hereinbefore mentioned lug 26 on the lower right side portion of the front face. The lower end of the sear bar has two cam surfaces 46 and 46' which are designed to function as hereinafter explained. Sear bar 21 is vertically mounted within slot I8a in the rear of breech block I as shown in Fig. 3. Sear bar 21 is mounted insuch a way that cam surface 46 engages and cooperates wtih cam surface 45 provided on sear slide 34.

Sear spring 30 is a leaf type spring, bifurcated as shown in Fig. 8. Such bifurcation provides two oppositely disposed arms 49 and 50. The solid end of such spring is provided with a vertical hole. 5|. Such hole is provided to mount spring 30 on pin I3 as has already been mentioned. Arm 50 of spring 39 restson top of lug 26 to bias sear bar 2'! downwardly and to secure such bar withinslot 13a. The other arm 49 of scar spring 30 rests on' shoulder 3| of sear I! .to bias such. sear downwardly and to securesuchsear within slots I8 and Mia.

Cam surface 46 of sear bar 21 incontact with cam surface 45 of slide 34 aids in retaining such slide. within. slot 32. The bias of spring pressed plunger 39 however is greater than that of arm 59 of sear spring 39 so that sear bar 21 will normally be in the raised-position shown in Fig. 3.

With the various components assembled to breech block I as above described, the firing pin is cocked by cockinglever 6. On the recoil stroke of breech block I when the firearm is fired, lever B is rotated clockwise from th positionshown in Fig. 2. The bottom end of such lever lies within the slot 8 of firing pin extension 4 and engages the rear surface 53 of such slot when the firing pin is in its firing position (to the right of the position shown in Fig. 2) whereupon rotation of such lever then forces firing pin 3 and firing pin extension 4 rearwardly so that sear I1 will drop down into. a notch 54 provided on the rear of firing pin extension 4 as shown inFig. 2 to. return the firing pin in cocked or retractedposition. On the counter recoil stroke lever 6 is rotated from the. position it was moved to during the recoil stroke of breech bolt I to the position shown in Fig. 2 whereby the lower end of lever *6 will permit the firing pin and firing pin extension to bedriven from the cocked position shown in Fig. 2 to the firing position. Thus the sear release mechanism is cocked and ready to fire as shown in Fig. 2.

Torelease sear H a transverse force is directed against the right end of sear slide 34 as. shown in Fig. 3 and such slide forced transversely tothe left across breech block I permitting notch 43 to. align with sear I'l. Sear slide 34 slides within transverse slot 24 provided on sear II. Itfollows that sear slide 34 blocks the upward move- 'ment of scar II whenever notches 43 and are not aligned with the sear or one of the ribs 35, for example lower left rib 35 as seen in Fig.2.. is so positioned as to be engageable with the lower surface defining the slot 24 inseam I1. However, when notch 43 is aligned with sear H, such sear will be .forced -upwardly by. the. bias-of spring 9 but only when sear slide 34 is no longer blocking sear ll. Hence the bias of spring 9 which is greater than that of sear spring 39 urges firing pin 3 and extension 4 forwardly thereby raisin sear l1. Such is possible because the slope of cam surface 23 on firing pin extension 4 and corresponding cam surface 22 provided on sear I1 is of such an angle as to permit firing pin extension 4 to slide out of engagement with sear ll. Thus firing pin 3 is biased forwardly to discharge a cartridge contained in the barrel of the firearm (not shown). Upon remova1 of the force utilized to move sear slide 34 transversely across breech block l, spring biased plunger 39 returns slide 3 2 to the neutral position shown in Fig. 3. Slide then locks sear H in engagement with firing pin extension i when such extension is in the cooked position.

The sear release mechanism shown herein is constructed and arranged to be fired from either the right or left side of the firearm. This is accomplished by reversing sear slide 34. That is, such slide can be assembled from either the right or left side of breech block i so that the actuating mechanism (not shown) can engage such slide from either the right or lei-t side of the firearm.

In Fig. 3 the sear release mechanism is arranged for release from the right side of breech block I. To release such mechanism from the left, sear slide 35 is assembled with the ends thereof reversed from that shown in Fig. 3. Notch 52 then faces upwardly so that sear bar 2! rests in such notch. In this position sear bar is inoperative, that is, such bar cannot be utilized to effect release of sear slide 34. slidably secures sear slide 34 to breech block I.

Sear I! can also be released from the top of block I. When release is desired from such position, sear slide 34 is assembled as shown in Fig. 3, that is, from the right. force is exerted on the upwardly projecting end of scar bar 21, cam surface 46 on the bottom end of such bar engages cam surface 45 on sear slide 34 thereby forcing such slide to the left as shown in Fig. 3 to effect release of sear I! from engagement with firing pin extension 4 as previously explained.

From the foregoing description, it is clearly apparent that there is hereby provided a light sear release mechanism for a firearm of the auslide from the scar and against the bias of rela- 5 tively weak springs that friction is maintained at a minimum and further that the force required to overcome the bias of the slide spring However, sear bar 21 When a downward is comparatively small with respect to that of a hammer spring or firing pin spring. It is further pointed out that the sear engages the firing pin in camming relation. Such camming surfaces are provided with a, comparatively greater slope so that the force required to cam the sear out of the path of the firing pin is comparatively small, yet when such sear is blocked by another relatively easy movable member, the sear will positively hold the firing pin in a retracted position until the blocking member is so moved as to permit the sear to be cammed out of engagement with the firing pin, thereby effecting the smooth release thereof.

I claim:

In a gun, a reciprocable breech bolt, a firing pin device provided with a cam surface adjacent its rear end and movable relative to the bolt, a vertically movable sear carried by the bolt and provided with a transverse slot across the rear face thereof and a lower cam surface complemental to the firing pin device cam surface and adapted to be elevated by the firing pin on forward movement thereof, resilient means adapted to depress the sear whereby said cam surfaces will interengage, a generally rectangular sear slide having end portions reversibly mounted in the bolt in rear of said sear and slidable through the transverse slot thereof, a pair of oppositely disposed ribs on either end portion of said slide which mount the slide in the bolt and one of which ribs is engageable with the lower surface defining the slot in said sear to prevent upward movement of the sear, resilient means carried by the slide and engageable with the sear to normally urge the slide into a position where said one rib will engage the sear to prevent upward movement, aforesaid, a downwardly inclined cam surface centrally provided on said slide, and a scar bar mounted on said bolt and sear for vertical movement and provided with a cam surface engageable with the cam surface on said slide operable upon downward movement of said bar to move said slide to a position where said one rib will be removed from the path of upward movement of the sear.

JOHN L. LOCHHEAD.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,498,542 Gorton June 24, 1924 1,530,702 Russell Mar. 24, 1925 1,949,418 Howard Mar. 6, 1934 1,981,855 Coupland Nov. 27,. 1934 

